Fluoroethylene carbonate as an important component in organic carbonate electrolyte solutions for lithium sulfur batteries

The benefits of fluoroethylene carbonate (FEC)-based electrolyte solution (1 M LiPF₆ in FEC/dimethyl carbonate (DMC)) over ethylene carbonate (EC)-based electrolyte solution (1 M LiPF₆ in EC/DMC) for the cycling of sulfur/carbon (S/C) composite cathodes were demonstrated for S/C composites prepared with two drastically different types of carbon hosts, micrometer-sized activated carbon powder (AC1) and carbonized polyacrylonitrile (PAN) cloth. The formation of solid electrolyte interphase (SEI) on the surface of the cycled S/C electrodes was demonstrated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).     

Effect of ether group on the electrochemical stability of zwitterionic imidazolium compounds

The cathodic stability of the zwitterionic imidazolium compounds was significantly enhanced by the introduction of an ether group at 1 or 2-position on the imidazolium ring. The cycle performance tests showed that the initial cell capacity was maintained almost unchanged up to 100 cycles at 0.5 and 1 C when 2.5 wt.% of 2-butoxymethyl-1-methylimidazolium-3-propylsulfonate or 2-butoxymethyl-1-butylimidazolium-3-propylsulfonate was added to the model electrolyte (1 M LiPF₆ in ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate (1/1/1 v/v/v)).Structures of zwitterionic compounds and their interactions with lithium ions were theoretically investigated.     

LiTFSI as a plastic salt in the quasi-solid state polymer electrolyte for dye-sensitized solar cells

Ionic conductivity and the type of ions are important for the composite polymer electrolyte (CPE) of the dye-sensitized solar cells (DSSCs). Lithium bis(trifluoromethane sulphone)imide (LiTFSI for short) which is easy to dissociate, is added in the composite polymer electrolyte(CPE) as a plasticizer. The LiTFSI acts differently from the conventional LiClO₄. LiTFSI changes the conformation of the polymer chain and shows higher ionic conductivity than LiClO₄. That contributes to the improvement of the short current density of the DSSC. Furthermore, the DSSCs with LiTFSI modification show higher photovoltage than the LiClO₄. The anions of TFSI^? prohibit the interface recombination more effectively compared with the LiClO₄ as the electrochemical impedance spectroscopy indicated. With the LiTFSI modified electrolyte, the performances of the DSSCs under 1 Sun, AM1.5 are improved and reaches the highest of 4.82% at the LiTFSI:LiI = 0.116:1, much better than the original DSSC(3.6%) and the LiClO₄ modified CPE electrolyte DSSC(4.32%).     

In situ fabrication of lithium polymer battery basing on a novel electro-polymerization technique

Electro-polymerization technology is proposed for the in situ fabrication of polymer lithium secondary battery and exciting results have been obtained. The polymerization starts from a common used electrolyte of 1 M LiTFSI in DOL/DME (2:1 by weight) with no initiator addition through a routine charge–discharge treatment under some appointed current rate. It is found that once an appropriate current is applied in the charging–discharging of Li/1 M LiTFSI in DOL + DME/LiCoO₂ cell, the original liquid electrolyte polymerizes readily during the first several cycles in an irreversible mode, and thus the desired polymer electrolyte obtained. SEM observation indicates that unlike previous report, the designed electro-polymerization does not result in destructive local break and then turnoff of the circuit, just the reverse, it helps to the formation of a smooth polymer layer, which can effectively protect the lithium substrate from corrosion and dendrite growth. Detailed examination shows that the in situ electro-polymerization does not disturb the electrochemical behavior of the cell, the cycleabilty, internal resistance are all comparable to that of a normal Li/LiCoO₂ liquid secondary battery.     

Suppression of dendritic lithium formation by using concentrated electrolyte solutions

This study examined the electrochemical deposition and dissolution of lithium on nickel electrodes in a propylene carbonate (PC) electrolyte containing different LiN(SO₂C₂F₅)₂ concentrations. The electrolyte concentration was found to have a significant effect on the reactions occurring at the electrode. The poor cycleability of the electrodes in the low-concentration solutions was improved considerably by increasing the electrolyte concentration. Transmission electron microscopy (TEM) revealed that a high-concentration solution produces a thinner solid electrolyte interphase (SEI) on the electrodeposited lithium than a low-concentration solution, e.g., ∼35 nm in 1.28 mol kg⁻¹ vs. ∼20 nm in 3.27 mol kg⁻¹ solutions. Raman spectroscopy showed that the solvation number of lithium ions differed according to the electrolyte concentration. This suggests that the structure of solvated lithium ions is an important factor in suppressing dendritic lithium formation.     

Cyclic carbonate based-electrolytes enhancing the electrochemical performance of Na4Fe3(PO4)2(P2O7) cathodes for sodium-ion batteries

Binary solvent mixtures containing NaClO₄ salt were investigated as electrolytes for sodium-ion batteries. The electrochemical performance of Na₄Fe₃(PO₄)₂(P₂O₇) cathodes was substantially improved when paired with an ethylene carbonate (EC)/propylene carbonate (PC)-based electrolyte. Our investigation revealed that EC/PC/1 M NaClO₄ exhibits superior oxidation durability at the cathode and is highly stable toward a Na-metal electrode.     

Development and implementation of a high temperature electrochemical cell for lithium batteries

An electrochemical cell designed to perform high temperature lithium battery tests has been developed adapting a typical Swagelok^® cell. The high temperature cell is intended to work in a wide temperature range, namely from room temperature up to 300 °C. It has been successfully tested at 250 °C using LiFePO₄ as cathode, LiTFSI as molten salt electrolyte and metallic lithium as anode.     

In situ atomic force microscopy study of exfoliation phenomena on graphite basal planes

In situ atomic force microscopy (AFM) was used to study the morphology changes of a highly oriented pyrolytic graphite (HOPG) electrode modeling the negative electrode used in commercial lithium-ion batteries. During the charge (lithiation) process in 1 M LiClO4 in ethylene carbonate:propylene carbonate (1:2) electrolyte we found that, degradation processes similar to the exfoliation of graphite also occur on basal planes. First a web-like structure of fine cracks develops which eventually results in local blister formation.     

“Water-in-Salt” electrolyte enabled LiMn2O4/TiS2 Lithium-ion batteries

High electrochemical reversibility of the TiS₂ anode in “Water-in-Salt” electrolyte (21 m LiTFSI in H₂O) is demonstrated for the first time. The wide electrochemical window and low chemical activity of H₂O in the “Water-in-Salt” electrolyte not only significantly enhanced the electrochemical reversibility of TiS₂ but also effectively suppressed the hydrolysis side reaction in the aqueous electrolyte. Paired with a LiMn₂O₄ cathode, the LiMn₂O₄/TiS₂ full cell delivers a relatively high discharge voltage of 1.7 V and an energy density of 78 Wh kg^− 1 as well as a satisfactory rate performance.     

Intermediate phases during alkali metal intercalation in HfNCl

The mechanism of the chemical and electrochemical alkali metal intercalation reactions in β-HfNCl has been investigated through electrochemical potential spectroscopy (EPS), in-situ powder X-ray diffraction during electrochemical intercalation and room temperature chemical intercalation experiments. EPS experiments in lithium cells reveal the presence of a plateau, at 1.8 V vs. Li⁺/Li⁰ accounting for ca. 0.14 mol Li, that indicates the formation of a new intermediate phase, and then a gradual decrease of potential with composition that extends up to very high lithium contents (ca. 1.1 per formula), consistent with the formation of a solid solution. Sodium electrochemical intercalation experiments showed a relatively similar behaviour with a plateau at 1.4 V vs. Na⁺/Na⁰, corresponding to ca. 1.7 V vs. Li⁺/Li⁰. In-situ monitored powder X-ray diffraction electrochemical intercalation experiments showed that the electrolyte solvent (ethylene carbonate/dimethyl carbonate, EC/DMC or propylene carbonate, PC) co-intercalated with the alkaline atom. This leads to a large expansion of the interlayer spacing that reaches a value of 21.06 Å in the lithium co-intercalated phase with EC/DMC, Li_x(EC/DMC)_yHfNCl, and 22.01 Å in the sodium co-intercalated phase with PC, Na_x(PC)_yHfNCl. Chemical intercalation using naphthyl-sodium solutions in tetrahydrofuran (THF) leads to solvent-free, multiple-phase samples showing in different proportions the pristine and the superconducting stage 2 and stage 1 phases. The composition of the intercalated samples depends on the pristine sample, the concentration of the naphthyl-sodium solution, the ratio Na:HfNCl and the reaction time. Pristine samples exhibiting low lithium intercalation degree upon electrochemical reduction gave the second stage as the major phase when treated with short reaction times or using low Na:HfNCl ratios, coexisting either with the host or with the first stage phase, whereas stage 1 is obtained as the major phase from pristine samples showing high electrochemical capacities. The staging behaviour and the multiphase nature of these samples account for the wide superconducting transitions and the different critical temperatures observed in these superconductors.     

A dual–ion battery using diamino–rubicene as anion–inserting positive electrode material

A novel and non-polymeric anion-inserting electrode material has been designed and prepared for promoting research on molecular ion rechargeable batteries: 5,12-diaminorubicene (DARb). The apolar core structure of a rubicene molecule has been coupled to two amino-groups for producing an original conjugated primary diamine exhibiting low affinity for polar solvents such as common carbonate-based battery electrolytes. The electrochemical reactivity of this organic molecule has been probed in a dual-ion cell configuration (vs. Li) using six different electrolyte formulations in terms of solvent (PC, EC-DMC) and lithium salt (LiPF₆, LiClO₄, LiTFSI). This diamino-rubicene material systematically showed a reversible electroactivity and promising performances when using 1 M LiPF₆ in EC:DMC (1:1 vol.%) as the electrolyte, such as an average potential of ~ 3.4 V vs. Li⁺/Li⁰, an initial capacity of 115 mAh·g^− 1 and a good capacity retention over 60 cycles without any optimization.     

Electrochemical properties of PABTH as cathode materials for rechargeable lithium battery

The electrochemical properties of polyanthra [1′,9′,8′-b,c,d,e] [4′,10′,5′-b′,c′,d′,e′]bis-[1,6,6a(6a-S^IV)trithia]pentalene (PABTH) were studied. It is found that PABTH exhibits a good cyclability and high capacity of 290 mAh/g in 1 M LiTFSI/DXL–DME (2:1 by weight) electrolyte. Detailed electrochemical characterization reveals that the capacity fading of PABTH within the first several cycles is due to the loss of ABTH monomer or its oligomer that is contained in PABTH in the form of soluble discharging products. It also needs to be noted that PABTH and ABTH has much higher charge–discharge efficiency (up to 95%) than that of sulfur (below 85%) because the S–S bond is fixed to the backbone.     

In situ AFM studies of SEI formation at a Sn electrode

Early stages of the solid electrolyte interphase (SEI) formation at a tin foil electrode in an ethylene carbonate (EC) based electrolyte were investigated by in situ AFM and cyclic voltammetry (CV) at potentials >0.7 V, i.e., above the potential of Sn–Li alloying. We detected and observed initial steps of the surface film formation at ～2.8 V vs. Li/Li⁺ followed by gradual film morphology changes at potentials 0.7 < U < 2.5 V. The SEI layer undergoes continuous reformation during the following CV cycles between 0.7 and 2.5 V. The surface film on Sn does not effectively prevent the electrolyte reduction and a large fraction of the reaction products dissolve in the electrolyte. The unstable SEI layer on Sn in EC-based electrolytes may compromise the use of tin-based anodes in Li-ion battery systems unless the interfacial chemistry of the electrode and/or electrolyte is modified.     

The effect of temperature and molar mass on the (liquid + liquid) equilibria of (poly ethylene glycol dimethyl ether + di-sodium hydrogen citrate + water) systems: Experimental and correlation

The (liquid + liquid) equilibrium for the {polyethylene glycol dimethyl ether 2000 (PEGDME₂₀₀₀) + di-sodium hydrogen citrate + H₂O} system was studied at T = (298.15, 308.15 and 318.15) K and atmospheric pressure (≈85 kPa). The free energies, enthalpies and entropies of cloud points were calculated in order to investigate the driving force formation of this two-phase system. To investigate the effect of molar mass of the polymer on the binodals and tie-lines, similar measurements were also made at T = 298.15 K on this two-phase system consisting of the PEGDME with molar masses of 500 and 250 g ⋅ mol⁻¹. The effective excluded volume model was used for representation of the phase-forming ability in PEGDME systems. An empirical and the Merchuck equations with the temperature dependency were used to correlate the binodal curves. The Othmer–Tobias and Bancraft and Setschenow equations, the osmotic virial and the extended NRTL models were used to fit the tie-line data.     

Protic ionic liquids as electrolytes for lithium-ion batteries

In this work we report for the first time about the use of protic ionic liquids (PILs) as electrolyte for lithium-ion batteries. The electrolyte 1 M LiTFSI in Et₃NHTFSI displays a conductivity comparable to that of aprotic ionic liquids, and electrochemical stability window large enough to allow the realization of LIBs containing LFP as cathode and LTO as anode. The use of this PIL as electrolyte in LIBs allows the realization of devices able to deliver good capacity and promising cycling stability.     

Novel poly (neutral red) nanowires as a sensitive electrochemical biosensing platform for hydrogen peroxide determination

Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H₂O₂ and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H₂O₂ at −0.1 V with a linear response range of 1 μM to 8 mM with a correlation coefficient of 0.996. The detection limit (S/N = 3) and the response time were determined to be 1 μM and <5 s and the high sensitivity is up to 318 μA mM⁻¹ cm⁻².     

Promising solvent of 12,12-diethyl-2,5,8-trioxa-12-silatetradecane for lithium secondary battery

A novel partly silanized ether solvent of 12,12-diethyl-2,5,8-trioxa-12-silatetradecane is proposed for Li/organo-sulfide or Li/S battery in this paper. It is superior to other ether solvent in high boiling point, high flash point and thus resulted high safety. The conductivity of it-contained electrolyte was measured to be 5.7 × 10⁻⁴ S/cm at 25 °C, which meets the requirement for practical application. Anodic polarization curve of it-contained electrolyte attests to its strong resistivity to electro-oxidation, and AC impedance measurement also approves that it has a good compatibility with lithium electrode. Cycling test of Li/1 M LiTFSI in 12,12-diethyl-2,5,8-trioxa-12-silatetradecane/PABTH cell indicates a good utilization of the active material in the new electrolyte system.     

Plastic–polymer composite electrolytes: Novel soft matter electrolytes for rechargeable lithium batteries

We present here a soft matter solid composite electrolyte obtained by inclusion of a polymer in a semi-solid organic plastic lithium salt electrolyte. Compared to lithium bis-trifluoromethanesulfonimide-succinonitrile (LiTFSI-SN), the (100 − x)%-[LiTFSI-SN]: x%-P (P: polyacrylonitrile (PAN), polyethylene oxide (PEO), polyethylene glycol dimethyl ether (PEG)) composites possess higher ambient temperature ionic conductivity, higher mechanical strength and wider electrochemical window. At 25 °C, ionic conductivity of 95%-[0.4 M LiTFSI-SN]: 5%-PAN was 1.3 × 10⁻³ Ω⁻¹ cm⁻¹ which was twice that of LiTFSI-SN. The Young’s modulus (Y) increased from Y → 0 for LiTFSI-SN to a maximum ∼1.0 MPa for (100 − x)%-[0.4 M LiTFSI-SN]: x%-PAN samples. The electrochemical voltage window for composites was approximately 5 V (Li/Li⁺). Excellent galvanostatic charge/discharge cycling performance was obtained with composite electrolytes in Li|LiFePO₄ cells without any separator.     

A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets

We demonstrate a highly efficient and large area synthesis of 2-D graphene nanosheets on the surface of flexible graphite foils by electrochemical exfoliation of graphite in an effective electrolyte, poly(sodium-4-styrenesulfonate) solution.A constant current of 150 mA/cm was applied to the vertically aligned graphite (anode) and copper (cathode) sheet in the PSS electrolyte solution during a preset time for electrolytic surface exfoliation of the graphite sheet; uniform expansion of the graphite foil was observed. This expanded foil was characterized using scanning electron microscopy, confocal laser scanning microscopy, and high-resolution transmission electron microscopy. Furthermore, we demonstrate the ability of this high surface area foil, covered with uniform graphene, to enable improved electrolyte permeability and Li ion transfer, thereby enhancing electrochemical performance of Li ion battery electrodes.     

Li/LiFePO4 batteries with room temperature ionic liquid as electrolyte

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP₁₄TFSI), which showed a wide electrochemical window (?0.1–5.2 V vs. Li⁺/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP₁₄TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO₄ cells initially delivered a discharge capacity of about 127 mAh g^?1 at a current density of 17 mA g^?1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.